The present invention relates to an explosion-proof hot water heater having an unsealed fuel combustion chamber and capable of detecting explosive vapours and shutting off the fuel burner with ample time delay before the explosive vapours can reach the combustion chamber.
Various attempts have been made in recent years to prevent the ignition of explosive vapours circulating about a hot water heater which is gas-fired, that is to say which is provided with a combustion chamber having a fuel burner therein. For example, it has been suggested to mount the hot water heater on an elevated support element, such as a rigid box or frame, and then to provide a gas sensor adjacent the floor area which is coupled to the gas shut off valve circuitry to shut the gas off upon detection of explosive vapours. Others have attempted to resolve this problem by providing a sealed combustion chamber with air combustion intakes being disposed elevated and communicating with the combustion chamber by ducts which are secured against the outer casing of the hot water heater. Usually this duct will extend several feet above the support floor. Again, gas sensors are provided to shut off the gas supply valve to the burner upon detection of explosive vapours. Screens have also been installed at air supply ports to act as flame arresters. These screens accumulate dust and clog up affecting adequate combustion air supply and therefore reducing the efficiency of the burner and emitting pollutant gas in the gas exhaust. These solutions have not proven feasible for the reason that some of these are costly, not practical in the real world, are subject to malfunction, affect the supply of sufficient combustion air to the combustion chamber, permit gas vapours to build up substantially before the burner is shut off and are generally not foolproof.
It is a feature of the present invention to provide an explosion-proof hot water heater with an unsealed fuel combustion chamber and capable of shutting off the gas supply to the burner at least a few minutes prior to the explosive gases reaching the air intake supply to the combustion chamber.
Another feature of the present invention is to provide an explosion-proof hot water heater of conventional type and having an unsealed fuel combustion chamber and wherein the novel feature of the hot water heater is simple in construction, economical, is integrated in the base construction of the heater housing, and easy to assemble.
According to the above features, from a broad aspect the, the present invention provides an explosion-proof hot water heater comprising an inner casing having conduit means to admit water in a water chamber thereof and to remove it therefrom. An outer skin casing is spaced from the inner casing with thermal insulation between the casings. The inner casing has a gas-fired combustion chamber at a lower end thereof. The combustion chamber has a sealed bottom wall and a circumferential side wall. A fuel burner is provided in the combustion chamber. Combustion air intake ports are provided in the circumferential side wall above the sealed bottom wall. A support base supports the sealed bottom wall elevated from a support surface. Air intake openings are provided about the outer skin casing spaced a predetermined distance above the sealed bottom wall. Air passage means communicates the air intake openings with the combustion air intake ports of the combustion chamber. A gas vapour sensor is secured in relation to the support base below the sealed bottom wall and is adapted to cause the burner to be shut off upon detection of explosive vapours.